Question

我遇到问题的函数是我在下面创建的函数DynamicString。该函数用于创建可变大小的字符串。

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如果有人可以修复我已创建的代码，那将非常有用。我知道可能有更好的算法，但我只是想知道我做错了什么。谢谢！

Answer 1

首先，正如其他人所指出的那样，正确的字符串结尾为'\0'，这是一个终止NUL字符。

其次，如果读取的第一个字符恰好是换行符，则永远不会执行循环。在free(*txt); *txt指向tmp NULL之后，您无法使用printf("\nThe entered string is : %s",*txt);，因为您正在取消引用NULL指针， c。

中的未定义的行为

第三，你有内存泄漏，因为在循环中你使用tmp将内存分配给malloc()，每次都会给你一个新的内存地址。这意味着在循环的每个循环中，tmp将有一个新地址，您将丢失旧地址，并且您无法再释放它。

如果要增加或减少指针指向的内存大小，请使用realloc。一个非常简单的示例如何使用realloc就像

#include <stdlib.h>
#include <stdio.h>


int main(void)
{
    int initalSize = 10;
    int increasedSize = 20;

    /*
     *  Because temp type is char, I left sizeof operator out. you can always write like
     *  char *sentence = malloc(initialSize * sizeof(*sentence)); or
     *  char *sentence = malloc(initialSize * sizeof(char));
     */
    char *sentence = malloc(initalSize);
    char *temp = NULL;

    /* 
     * Malloc can return a NULL pointer. You need to check sentence value before using it
     * elswhere in the code.
     */
    if (!sentence) {
      printf("Memory allocation failed for sentence\n");
      exit(EXIT_FAILURE);
    }

    // Some code here...

    /*
     * Realloc can also return a NULL pointer. Need to use a temporary
     * pointer. In case realloc really returns NULL, and you don't use a temporary pointer and
     * use it like "sentence = realloc(sentence, increasedSize);", you will have a memory leak
     * because now sentence = NULL and you don't have a pointer that points to the old memory.
     *
     */
    temp = realloc(sentence, increasedSize);

    // Also need to check temporary pointer value.
    if (!temp) {
      printf("Allocating more memory to sentence failed\n");

      // One of the possible solutions. You can always use the value that you already have in sentence;
      free(sentence);
      exit(EXIT_FAILURE);
    }

    /*
     * If everything was ok, you make sentence point to the same address in memory as temp was pointing.
     * What it means is that you give ownership of the memory temp points to the sentence.
     */
    sentence = temp;

    // Some code here...


    // No need for sentence anymore
    free(sentence);

    /*
     * It is always recomended to make unused pointers that you don't use anymore or if you have
     * freed them to point to NULL;
     * It makes sure that those pointers no longer point to the previous memory addresses. Remember that
     * free only frees the memory where sentence and temp pointed to.
     *
     * If you don't make them point to NULL, then sentence and temp would be called a dangling pointer.
     *
     */
    sentence = NULL;
    temp = NULL;

    // Some code here...

    return 0;
}

如果您使用Linux，最好使用名为Valgrind的程序检查代码。它有助于检测内存泄漏和内存错误。

此外，要阅读stdin中的字符，我会使用getchar()。它更简单，更快捷。 Stack Overflow中的一小部分信息回答here。

最后一点，如果你使用的函数不返回任何内容，你就不需要在函数的末尾写return。

c中的动态字符串分配

1 个答案: